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forces (p5) Flashcards

1
Q

what is a scalar quantity, and give an example:

A
  • scalar quantities only have a magnitude (size). they do not have a direction.
  • mass, temperature, speed, distance, time, energy.
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2
Q

what is a vector quantity, and give an example:

A
  • vector quantities have both a magnitude (size) and a direction.
  • displacement, weight, force, velocity, acceleration, momentum.
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3
Q

how can you represent vectors using an arrow?

A
  • the length of the arrow represents the magnitude of the vector
  • the direction of the arrow represents the direction of the vector
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4
Q

what are contact forces, name an example:

A
  • the two objects are physically touching
  • e.g. friction. force of friction acting between water and aeroplane. causes aeroplane to slow and come to a stop
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5
Q

what are the 4 contact forces?

A
  • friction
  • air resistance
  • tension
  • reaction force/normal contact force (force that pushes touching objects apart).
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6
Q

what is a normal contact force?

A
  • e.g. lamp on a table. lamp is exerting downward force on table (weight). table is exerting upward force on lamp (normal contact force).
  • normal contact force can only happen if the two objects are in direct contact
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7
Q

what are non-contact forces, name some examples:

A
  • two objects are physically separated
  • e.g. gravitational force attracts all objects to other objects
  • e.g. electrostatic force is the force between 2 charged objects (force of attraction/repulsion)
  • e.g. magnetic force is the force experienced by certain objects in a magnetic field
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8
Q

what are the 4 non-contact forces?

A
  • gravitational
  • electrostatic
  • magnetic
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9
Q

what is gravity?

A

the force of attraction between any two objects that have mass

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10
Q

describe magnetic and electrostatic forces:

A

can be attractive or repulsive
- electrostatic is between two charged objects

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11
Q

describe negative vector arrows:

A
  • the length of the arrow shows the magnitude. the direction of the arrow shows the direction
  • if you had an vector of 2km west, it could also be written as -2km east, as it’s backwards in the east direction
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12
Q

what is the equation for work done?

A

work done = force x distance
- the distance must be in the line of action of the force

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13
Q

what happens when you apply the brakes to a car?

A

a moving object has kinetic energy. during braking, the brake presses against the wheel, and a force of friction acts between the brake and the wheel. the kinetic energy store of the car is transferred to thermal energy store in the brakes. temperature of the brakes increases, speed of the car decreases (loses kinetic energy).

the greater the speed, the greater the braking force needed to stop the car in a certain distance.
- kinetic energy = 1/2 x mass x velocity ^2
- so doubling the velocity of the car, the kinetic energy quadruples. more kinetic energy needs to be converted, and this takes longer.

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14
Q

what is the potential risk of applying a large braking force?

A

transfers a lot of thermal energy to the brakes, causing them to overheat. the driver could lose control of the vehicle.

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15
Q

what is gravity?

A

force of attraction between all objects. non-contact force. vector quantity.

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16
Q

define ‘mass’:

A
  • a measure of the amount of matter in an object.
  • not determined by gravity, so stays the same wherever you are in the solar system.
  • is not a force.
  • kg
  • scalar quantity
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17
Q

define ‘weight’:

A
  • a measure of the force of gravity acting on an object.
  • determined by the gravitational field strength (measure of the force of gravity in a particular location), so changes depending on where you are in the solar system.
  • objects on the surface of the Earth experience a force of 9.8N/kg per every 1kg of their mass.
  • is a force.
  • N
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18
Q

what is the equation to calculate the weight of an object?

A

weight = mass x gravitational field strength

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19
Q

what is the relationship between weight and mass?

A

directly proportional. doubling the mass means the weight also doubles.

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20
Q

how do you determine an object’s weight?

A

use a calibrated spring balance (newtonmeter).

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21
Q

what happens to an object when you apply a force to it?

A
  • compress
  • stretch
  • bend
  • if you want it to stay still, you must apply more than one force
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22
Q

what is the relationship between force and extension?

A

directly proportional
- however, exactly how much the spring extends for a given force depends on the object’s spring constant

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23
Q

what is the spring constant?

A

tells us how many newtons it would take to stretch the object by 1m. the higher the spring constant, the stiffer the object, as it requires more force to stretch it.

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24
Q

define energy transfer and work done:

A
  • whenever a force is used to move an object, energy is transferred. scientists call this work.
  • work is simply a measure of energy transfer, so the unit of work is the joule. when a force of 1N moves an object by 1M, 1J of work has been done.
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25
Q

define ‘centre of mass’:

A

the weight of an object may be considered to act at a singular point.
- however, the centre of mass of an object may not necessarily be in its centre; this would only occur if the object is uniform in shape and density.

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26
Q

when you balance an object on one point, what determines when it topples over?

A

let’s say a square is balancing on one corner. as it’s uniform in shape and density, the centre of mass is in its centre.
- if you were to push the object, but its centre of mass doesn’t surpass the point of contact, it falls back.
- if you were to push the object, and its centre of mass surpasses the point of contact, it falls forward, as it is unbalanced.

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27
Q

define ‘elastic deformation’:

A

when objects deform elastically (stretching/compressing/bending), they still hold the ability to return to their original shape if we take away the forces acting on them.
- Hooke’s law (where force and extension are directly proportional) only works when an object behaves elastically.

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28
Q

how do you change an object’s length/shape?

A

apply more than one force. applying only one force to a stationary object means that the forces are no longer balanced, and the object would simply move.

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29
Q

define ‘plastic/inelastic deformation’:

A

when objects deform plastically, they can no longer quite return to their original shape. they have reached their limit of proportionality/elastic limit.

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30
Q

what is the equation to calculate the force needed to stretch an elastic object?

A

force = spring constant x extension/compression

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31
Q

what is the equation to calculate elastic potential energy, and what is it?

A

elastic potential energy = 1/2 x spring constant x extension squared
- elastic potential energy is the energy transferred to an object as it’s stretched

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32
Q

what can you take from a graph with force plotted against extension?

A
  • the gradient is the spring constant (but only the straight part)
  • the area under the line is the elastic potential energy
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33
Q

what is the relationship between work done and elastic potential energy?

A

they’re equal, as long as the object is not inelastically deformed.

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34
Q

what are the three variables for the Hooke’s law required practical?

A
  • independent (x axis):
    force applied
  • dependent (y axis):
    extension of spring
  • control:
    room temperature, diameter of spring, starting length of spring, spring material
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35
Q

describe the method for the Hooke’s law required practical:

A
  1. measure original length of the spring using a ruler.
  2. set up the equipment as shown in the diagram (you should be able to picture the set-up).
  3. attach a known weight (1N) to the spring. wait for the spring to stop moving.
  4. measure the new length of the spring.
  5. calculate the extension of the spring by subtracting the original length from the new length of the spring.
  6. repeat steps 2-4 with weights up to 5N.
  7. plot a scatter graph with the force on the x axis and the extension on the y-axis. the graph should show a directly-proportional relationship.
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36
Q

what is the biggest source of uncertainty in the Hooke’s law required practical?

A
  • the biggest source of uncertainty is in the measurement of the spring, using the human eye. a parallax error (random error) could occur, so you must get to eye-level to obtain the most accurate reading.
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37
Q

what has occurred if the line of best fit on a Hooke’s law graph stops being straight?

A

this shows that the spring has reached its elastic limit. it has become plastically deformed, and has therefore skewed the results of the practical, as Hooke’s law only works when the object is elastically deformable.

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38
Q

what is Hooke’s law?

A

force is directly proportional to extension.
- as an equation, this is F = ke, where k is a constant.
- force (N), spring constant (N/m), extension (m).

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39
Q

describe the pressure in a column of fluid:

A
  • take a column of water. the water at the bottom of the column would be under a much higher pressure than the water at the top. the mass of the particles pushing down on the water at the bottom of the container creates more pressure.
  • the deeper the liquid, the greater the pressure.
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40
Q

describe the atmosphere:

A
  • thin layer of air (nitrogen, oxygen, greenhouse gases) around the Earth.
  • contains the ozone layer, which keeps out the most harmful radiation
  • most dense at the surface of the Earth; greater number of air particles per given volume.
  • gets less dense as you increase in altitude.
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41
Q

what is atmospheric pressure?

A

the total force of all the air particles constantly colliding with something from all sides

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42
Q

describe how atmospheric pressure changes with elevation:

A
  • an object at sea level has more air particles surrounding it than an object 1000m in the air
  • more air particles around an object means more collisions, therefore a greater force exerted on the object, therefore higher pressure
  • an object at sea level is effectively at the bottom of the atmosphere, so will have a huge weight of lots of particles pressing down on it. weight is also a force, contributing to its pressure
  • atmospheric pressure decreases as elevation increases
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43
Q

why must mountaineers carry oxygen cylinders with them when climbing a mountain?

A

the air is so thin with so few particles that there aren’t enough oxygen molecules to breathe in

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44
Q

what is a fluid?

A

a material that can flow. e.g. liquids, gases.

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45
Q

how do you calculate the pressure of a fluid?

A

pressure = force applied to a surface / area of that surface.

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46
Q

how do fluids (gases and liquids) interact with container walls?

A
  • gas particles are widely spaced and move rapidly. they collide with the container walls, exerting right-angled forces, creating pressure
  • liquid particles also exert forces at right-angles to the container walls and to the air particles at the surface, creating pressure
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47
Q

how come a particle colliding with a wall at a perfect right angle exerts the most pressure?

A
  • its entire force is used to generate pressure on the container wall
  • a particle that is hitting the container wall diagonally, only a small component of its force will be perpendicular to the container (split the force into vertical and horizontal components). a much smaller force is used to create pressure
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48
Q

how do you calculate the pressure of a column of liquid?

A

pressure = height of column of liquid above the object (depth) x density of liquid x gravitational field strength

49
Q

where does the pressure acting on an object in a liquid come from?

A
  • all the surrounding water molecules colliding with it
  • all of the weight of the water molecules above it, felt as a downward force
50
Q

why does the pressure of a liquid increase with depth?

A
  • as the depth increases, there is a greater weight of liquid acting downwards, therefore pressure increases
  • the pressure also increases with the density of the liquid, as more dense liquids have a greater weight acting downwards.
51
Q

what are the 4 factors affecting the pressure experienced by an object in a fluid?

A
  • water molecules colliding with object
  • weight of liquid on top of the object
  • density of the liquid (the denser the liquid, the larger the mass per unit of volume, therefore the larger the weight)
  • the gravitational field strength (the larger, the larger the weight, as it determines the weight for a given mass)
52
Q

describe upthrust:

A
  • think of an object fully submerged in liquid.
  • pressure of a liquid depends on the depth. the bottom of the object is deeper than the top, so it experiences a larger upwards force from the bottom than a downwards force from the top. resultant force acting upwards and this is upthrust.
  • for an object to float, the upthrust must equal the object’s weight.
  • if the upthrust is less than the weight, the object sinks.
53
Q

describe floating and sinking in more detail:

A

LESS DENSE THAN WATER:
- upthrust equals weight of object, it floats
- floats high in the water

SAME DENSITY AS WATER:
- the object floats (density of liquid = density of object)
- the surface of the object is at the surface of the water

MORE DENSE THAN WATER:
- cannot displace volume of water equal to its own weight
- weight of object greater than upthrust, it sinks

54
Q

describe ‘speed’:

A
  • speed of an object tells us the distance the object has travelled in a given time.
  • scalar quantity, because it doesn’t involve direction.
55
Q

what are the typical walking, running, and cycling speeds?

A

typical walking speed: 1.5 m/s
typical running speed: 3 m/s
typical cycling speed: 6 m/s

  • however, these can depend on several factors: age, health, terrain, distance travelled, their effort
56
Q

recite the three typical vehicle speeds:

A

car on main road: 25 m/s
fast train in the UK: 55 m/s
cruising aeroplane: 250 m/s

  • however, these vehicles rarely continue to travel at a constant speed. for example, cars slow down and speed up at different points in their journeys.
57
Q

what is the speed of sound in air?

A

330 m/s

  • however, it can vary. sound travels faster on warmer days than cooler ones, and its speed can change when travelling through different mediums
58
Q

what is the range of speed of wind?

A
  • wind is the natural movement of air
  • can be between 0m/s and over 55m/s (faster than a fast train)
  • this depends on temperature, atmospheric pressure, and the structures it’s travelling past (buildings/mountains)
59
Q

how do you find the average speed/velocity across an entire journey from a distance-time graph?

A

total distance/displacement / total time.

60
Q

what is the equation for velocity?

A

velocity = displacement / time

61
Q

how do you find the instantaneous speed from one point on a distance-time graph?

A

find the gradient of a tangent touching the curve of the specified time on the graph.
- pick two points on the tangent, and divide the change in distance by the change in time. the gradient of this tangent is equal to the gradient (speed of the object) of the curve at that point

62
Q

how do we interpret distance time graphs?

A
  • gradient at any point tells us the speed at which the object is travelling (gradient = change in distance / change in time, which is the formula for speed)
  • a straight line means a constant speed
  • a flat line means the object is stationary. no gradient means no speed
  • increasing gradient means acceleration, decreasing gradient means deceleration
63
Q

how do we interpret velocity time graphs?

A
  • the gradient is equal to the change in velocity / change in time, which is the formula for acceleration. the gradient = the acceleration
  • a constant positive gradient shows a constant positive acceleration. a constant negative gradient shows a constant negative acceleration (deceleration)
  • flat sections of the graph have a gradient of 0, so aren’t accelerating. they’re travelling at a constant velocity
  • a curve that is getting steeper means that the gradient is increasing, therefore the rate of acceleration must also be increasing
64
Q

how do you find the total distance travelled on a velocity time graph?

A

find the area under the line
- you can split it into triangles and rectangles, to make it easier to calculate
- under a curved line, you must roughly count how many squares there are, and convert that into metres

65
Q

what is a moment?

A

the turning effect of a force. these bring motion about a turning point, called a pivot or a fulcrum (e.g. seesaw, wheelbarrow, crane, spanner).

66
Q

what is the equation to calculate the moment of a force?

A

moment (Nm) = force x distance
- the distance must be perpendicular to the place where the force is being applied to the pivot
- therefore to get a bigger moment, apply a big force far away from the pivot. if you applied a force closer to the pivot, you’d have to generate a bigger force to get the same turning effect

67
Q

are moments a vector or a scalar quantity?

A

moments are vector quantities. these can either be clockwise or anti-clockwise, describing the resulting motion the force might cause about the pivot.
- if the clockwise and anti-clockwise moments are equal due to the weights acting on them, the moment is balanced.

68
Q

what do levers do?

A

transmit the turning effect of a force from one side of the pivot to the other. they’re force multipliers.
- we apply a small input force, and this creates a much larger output force somewhere else

69
Q

what are the three components of a lever?

A
  • load
  • effort
  • turning point (e.g. pivot, fulcrum)
70
Q

describe the motion of scissor blades, and how they differ to wheelbarrows:

A

because the input and output forces are on different sides of the pivot, they’ll act in different directions. in this case, one up and one down.

  • this is the opposite to wheelbarrows, for example, as both the input and output forces are on the same side of the pivot, so they’ll both act in the same direction (up).
71
Q

which is generally closer to the pivot, the output or the input force?

A

the output force, meaning that there’ll be a larger force. this is the whole point of levers - we can get a large output force, with a relatively small input force.

72
Q

what is the role of a gear?

A

gears have the role of transmitting turning effects.

73
Q

describe a gear, using examples of gear a and gear b:

A
  • two interconnected gears: gear a and gear b.
  • gear a is connected to the engine, which provides it with a turning force so that it rotates.
  • gear b is connected to the wheels of the vehicle, so if gear b rotates due to gear a’s rotation, then the wheels will rotate too.
  • the gear system transmits the turning force from the engine to the wheels.
74
Q

what are two important notes about gears?

A
  • gear a and gear b will always turn in opposite directions (one clockwise and anti-clockwise).
  • the gears are always different sizes. the radius of gear b is two times larger than the radius of gear a. this means that gear b’s turning effect is two times bigger than that of gear a. therefore the turning effect of the engine has been doubled as its passed to the wheels.
    > however, gear a must rotate 2x for
    every rotation of gear b. therefore the
    total work done remains the same.
75
Q

what is a force (N)

A

a push, a pull, or a twist that acts on an object due to an interaction with another object.
- has both magnitude and direction (vector quantity).

76
Q

what is a resultant force?

A

single force that has the same effect as all of the original forces acting together. to work it out, subtract the smaller force from the larger force.
- e.g. block pushed to the right, force of 20N. friction to the left, 10N. resultant force is 10N, as 20-10=10.

77
Q

which two properties of an object may be affected by a resultant force?

A

the speed and the direction

78
Q

describe a free-body diagram:

A

  • object drawn as a point
  • forces are drawn as arrows starting at the point
  • the length of the arrow shows us the size of the arrow, and it’s direction shows the force’s direction
  • some of the forces may cancel each other out, and what we have left is the resultant force (overall force on an object)
  • if all the forces acting on an object balance out, we’d say it’s in equilibrium
79
Q

what does a diagonal vector arrow mean?

A

part of the force is acting horizontally, and part is acting vertically.

80
Q

how do you find the resultant force from two vector arrows?

A
  • place the arrows tip to tail
  • draw a hypotenuse, creating a triangle and connecting them. measure the length of this line for the magnitude
  • to find the direction, measure the bearing of the hypotenuse
81
Q

how do you know if the forces are in equilibrium?

A

the forces may all balance. to find out if this is the case, when connecting all of the arrows tip to tail, they will form a perfect triangle, and this means they’re in equilibrium

82
Q

what is the equation for speed?

A

speed = distance / time

83
Q

what happens to the velocity when an object moves in a circle at a constant speed?

A

its velocity is constantly changing, as the direction is constantly changing, despite the speed remaining constant. (includes moving around a corner).

84
Q

what is acceleration?

A

the rate of change in velocity

85
Q

what is the equation to calculate average acceleration?

A

acceleration (m/s^2) = change in velocity (m/s) / time (s)

can also be written as:

acceleration = (final velocity - initial velocity) / time

  • only an average acceleration, as we can’t be sure that the acceleration is uniform/constant. could have accelerated lots in the first few seconds
86
Q

can vector quantities be negative?

A
  • yes, examples include acceleration and velocity
  • them being negative suggests that they’re slowing down
87
Q

what does the area under a velocity-time graph line represent?

A

the displacement (not distance!!).
- with many different constant segments, calculate their individual areas, then add them together.
- when there are many different not constant segments, you count the approximate number of squares under the graph. calculate the area of each square, and multiply that by how many there are.

88
Q

how do you calculate the constant acceleration of an object?

A

(final velocity)^2 - (initial velocity)^2 = 2 x acceleration x distance
- this includes distance instead of time, like in the other acceleration equation

89
Q

when can we assume an object’s acceleration?

A
  • if an object is dropped, e.g. a ball
  • it can accelerates at 9.8m/s^2, due to the force of gravity
90
Q

what happens when an object falls through a fluid?

A
  1. jumps out of plane.
  2. when any object falls towards surface of the Earth, it initially accelerates at 9.8m/s^2, due to the force of gravity acting on the object. the only force acting is weight. resultant force acting downwards, accelerate towards the ground.
  3. as the skydiver falls, he experiences an upward force of friction with the air particles (air resistance). however, this force won’t be too great, as their velocity is still quite low. the weight is still greater, so he continues to accelerate downwards.
  4. as velocity increases, air resistance also increases. after some time, the force of air resistance balances the force (no resultant force) due to gravity. the object stops accelerating and moves at a constant velocity (terminal velocity).
    - the terminal velocity that an object reaches depends on the object (some may experience a greater force of friction due to their shape).
  5. skydiver opens parachute - surface area now increases, air resistance massively increases. it’s greater than weight, so the resultant force is acting upwards. he decelerates, and air resistance decreases.
  6. weight and air resistance balance again, resultant force is 0, velocity remains constant (lower terminal velocity)
  7. they then reach the ground
91
Q

what are the two factors that can affect air resistance?

A
  • surface area: the higher the surface area, the larger the area over which collisions can take place
  • velocity: the faster they’re moving, the more particles they’ll collide with
92
Q

what is Newton’s first law of motion?

A
  • if the resultant force acting on a still object is 0, it’ll remain stationary
  • if the resultant force acting on a moving object is 0, the object will continue moving at a constant velocity

the velocity of an object will only change if a resultant force acts on the object. this is also known as inertia.

93
Q

how can a resultant force affect an object’s speed?

A

causes it to change. can speed it up (pushing it), slow it down (pushing against it), make it accelerate upwards (acting on the bottom of the object).

94
Q

what is Newton’s second law of motion?

A

the acceleration of an object is directly proportional to the resultant force acting on the object (greater force, greater acceleration), and inversely proportional to the mass of the object (larger mass, smaller acceleration).
- if a non-zero resultant force acts on an object, it will cause it to accelerate

95
Q

what are the 5 things that could happen to an object when a resultant force to the right acts on it?

A
  1. if the object is stationary, it will start moving to the right
  2. if the object is moving to the right, it will speed up
  3. if the object is moving to the left, it will slow down
  4. if the object is moving slowly to the left, it will stop
  5. the object could change direction. acceleration is the change in velocity / change in time, and velocity is determined by speed and direction. any change in the direction of the object also changes the velocity, so it’s considered acceleration
96
Q

how do you calculate the force needed to accelerate an object? (Newton’s 2nd law)

A

(resultant) force = object’s mass x acceleration

97
Q

what is inertial mass?

A

measure of how difficult it is to change the velocity of an object. an object with a large inertial mass will require a larger force to produce a given acceleration than an object with a smaller inertial mass.
- inertia (basically Newton’s 1st law) is the tendency for the motion of an object to remain unchanged unless a resultant force acts on it

98
Q

how do we calculate inertial mass?

A

inertial mass = force / acceleration
- the equation for newton’s second law

99
Q

what is Newton’s third law?

A

whenever two object interact, the forces they exert on each other are equal (magnitude) and opposite (direction).
- pushing on a wall and the wall pushing back is called normal contact force
- e.g. paddle pushing through water. water pushes back on paddle. forces are equal in magnitude, but opposite in direction.
- for an object to be accelerated or moved, you need a high force or a small mass, and this determines whether you or a heavy object will move when you push against one

100
Q

what is the stopping distance, and the two parts?

A

total distance travelled from when the driver first spots the obstruction to when the car stops. the greater the speed of the vehicle, the greater the stopping distance, assuming the braking force is the same.
- total stopping distance = thinking distance + braking distance

thinking distance:
distance travelled by the car during the driver’s reaction time (time taken for driver to spot obstruction, make a decision, then start to brake)

braking distance:
distance car travels from when the brakes are applied to when the car stops. speed of the car increases, braking distance increases

101
Q

how can we measure a person’s reaction time, as it varies from person to person?

A

1 person holds ruler. person places fingers either side. ruler is dropped, person must catch it. the further the ruler falls before it is caught, the longer the reaction time.
- by measuring the distance the ruler fell, we can look up a the reaction time in a table.

102
Q

what factors can affect reaction time?

A

fatigue, alcohol, certain drugs, distractions in the car (e.g. mobile phone).
- these therefore increase the thinking distance.
- the speed at which the vehicle is travelling also increases the thinking distance (longer it takes to brake, further you travel)

103
Q

what factors can affect the braking distance?

A
  • wet or icy conditions reduce the friction between the tyres and the road which can cause the car to skid
  • if the car has worn tyres (reduces friction)
  • worn brakes
  • travelling at a higher speed and a car with higher mass both increase the car’s kinetic energy, which must be reduced to 0 for the car to stop
104
Q

how do thinking and braking distances change with speed?

A
  • thinking distances increase directly proportionally with speed
  • braking distances increase much more dramatically - the braking distance increases 4 fold
105
Q

which objects have momentum?

A

all moving objects have momentum. stationary objects have no momentum.

106
Q

is momentum a vector or scalar quantity?

A
  • vector
  • either forwards (+) or backwards (-) /to the right or left
107
Q

what is the symbol for momentum, and what are its units?

A
  • the greek letter rho, a p
  • units are kg m/s
108
Q

what happens to the momentum of the object if you hit it?

A
  • it will accelerate
  • its velocity will increase
  • its momentum will therefore increase
109
Q

what is the equation for momentum?

A

momentum (kg m/s) = mass x velocity

110
Q

what is the law of conservation of momentum?

A

in a closed system, the total momentum before an event is equal to the total momentum after an event.
- cannon and cannonball stationary, total momentum is 0. cannonball fired with great forwards momentum. cannon kicks back with great backwards momentum. overall momentum is still 0, momentum has been conserved.

111
Q

describe car crashes and crash tests:

A
  • during a car crash, the momentum of the passengers falls from a large amount to 0 in less than a second. places huge forces on the passengers and can be lethal (head trauma, spinal damage). we can reduce this danger by making the change in momentum happen over a longer period of time, reducing the force the passenger will experience
112
Q

how do you calculate the forces acting on a passenger during a car crash?

A

force = change in momentum (mass x velocity) / time

113
Q

describe some safety devices which slow down momentum change:

A
  • airbags
  • seatbelts
  • crashmats
  • bike helmet
  • cushioned surfaces
114
Q

what are crumple zones?

A
  • at the front and back of a car, and crumple on impact
  • instead of the car stopping immediately, there is a small amount of extra time for the car to lose momentum as it crumples
115
Q

what are the functions of seatbelts and airbags?

A
  • stops the passenger from flying out of the car as it stops
  • ## slightly stretchy, so you slow down a bit more slowly
  • airbags are compressible like a pillow (contrasting to the hard dashboard), and so also slow down the rate at which you lose momentum
116
Q

when may the momentum be 0 before and after an event?

A
  • at the beginning, the momentum of a gun may be 0, as it starts of stationary
  • the bullet is then fired, and has momentum in the forwards direction. to compensate for this, the gun recoils back with equal momentum, so the total is still 0
117
Q

how do we work out how much force is required to cause a change in an object’s momentum?

A

force = change in momentum (final momentum - initial momentum) / time for change to take place

can be written as:
F = (mv - mu) / t

118
Q

what is the formula for change in momentum?

A

change in momentum = (mass x final velocity) - (mass x initial velocity)

physics (8 decks)

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